<!DOCTYPE html>
<style>
.box {
  width: 200px;
  height: 200px;
  margin: 20px;
  background-image: radial-gradient(transparent, black);
  filter: url(#lighting);
}
</style>
<div class="box"></div>
<svg width="0" height="0">
  <filter id="lighting" x="-0.5" y="-0.5" width="2" height="2">
    <feDiffuseLighting surfaceScale="200">
      <feDistantLight azimuth="135"/>
    </feDiffuseLighting>
    <feComposite operator="in" x="50" y="50" width="100" height="100" in2="SourceGraphic"/>
  </filter>
</svg>
